1. Field of Invention
This invention pertains to the catalyzed preparation of a chalcogenide glass and to chalcogenide glass having three or more components.
2. Background of Invention
Semicoductor materials, such as the sulfides of group IV(b) elements are promising materials for electronic devices and can be used for light transmission in the middle and far infrared spectral range since they are transparent to wavelengths from 2-15 .mu.m. They also have low intrinsic transmission losses. For instance, germanium disulfide has ten times lower absorption than silica in the far IR region.
The electronic and optical properties of semiconductors are strongly affected by impurities and inhomogeneities in the material most of which are a result of the preparation process. By using an appropriate preparation, the light transmission losses of the prepared material can be minimized to the level of intrinsic optical losses based on the pure material properties.
The best material for light transmission applications would be a monocrystal, in order to minimize loss and maximize transparency. Since it is very difficult to produce a monocrystal in a desired shape, such as a fiber or a film, glasses are used to overcome these shortcomings.
Glass is a hard, amorphous, inorganic, usually transparent, brittle substance made by fusing silicate precursors, sometimes borate and phosphate precursors, with certain basic oxides and then rapidly cooling to prevent crystallization. The high temperature typically used in making glass is responsible for high level of impurities e.g., crucible materials, and limits the glass to components that can withstand the high temperatures. This means absence of organic components.
Similarly, chalcogenide glasses, such as As.sub.2 S.sub.3, As.sub.2 Se.sub.3 and Ge.sub.30 As.sub.10 Se.sub.30 Te.sub.30, are typically made by heating the elemental starting materials in quartz ampules at temperatures between 750-1100.degree. C. This also leads to impurities due to crucible reactions. Therefore, there is need for a low temperature process to make chalcogenide glasses.
The first attempt to synthesize a colloidal metal sulfide, an optical material, at room temperature using a low temperature process was done more than fifteen years ago. At that time, monodispersed cadmium sulfide was synthesized using cadmium nitrate and thioacetamide. By controlling the reaction conditions such as pH, concentration, temperature, and the nature of the anions, particle nucleation and growth were controlled to obtain a monodispersed cadmium sulfide sol.
A couple of years following the first attempt, an effort was made to sythesize metal sulfides from metal alkoxides and hydrogen sulfide. Using a sol-gel process, a germanium sulfide gel was produced by reacting germanium tetraethoxide dissolved in toluene with hydrogen sulfide gas bubbled through the solution. Since alkoxides easily hydrolyze, the reaction apparatus was previously purged with an inert gas. The reaction product was germanium sulfide gel with significant germanium oxide impurities. Subsequently, it was shown that the product was not pure germanium sulfide but a mixture of germanium sulfide and germanium oxide due to the presence of water as an impurity.
Others in the past have used organometallic compounds of zinc, aluminum and magnesium, and hydrogen sulfide as precursors. Metal sulfide particle aggregates were obtained.
Lanthanum sulfide was also made by bubbling hydrogen sulfide through lanthanum isopropoxide in dry benzene, as the solvent. The powder obtained was heat-treated in hydrogen sulfide finally producing single-phase crystalline lanthanum sulfide (La.sub.2 S.sub.3).
Amorphous particles were also prepared by reacting titanium tetrapropoxide [Ti(OC.sub.3 H.sub.7).sub.4 ] and hydrogen sulfide. Resulting powder was heat-treated in flowing hydrogen sulfide to produce crystalline titanium sulfide (TiS.sub.2).
Considerable success has been achieved in terms of the solution synthesis of metal sulfides. The sol-gel process could be expected to provide a homogeneous product with a low level of impurities.